In general, characteristics of a radiation detector, such as gain or quantum efficiency, are varied with a counting rate of radiation incident on the radiation detector. For example, considered is a pulse signal output from the radiation detector. When the counting rate of radiation incident on the radiation detector is varied, a width and a wave height of the pulse signal output from the radiation detector are varied even if radiation having the same level of energy is incident on the radiation detector. In this case, a maximum value of an energy histogram of the measured radiation is also varied, resulting in degradation in energy resolution of a radiation detection apparatus.
Therefore, it is necessary to correct a variation in characteristics of the radiation detector due to the counting rate variation so as to prevent the degradation in energy resolution of a radiation detection apparatus.